stefnotch/quantum-sheet

Floats not always desired?

phcreery opened this issue · 2 comments

phcreery commented

Example:

>>> _HI = sympy.symbols('a')
>>> sympy.expand(sympy.Pow(sympy.Add(_HI,sympy.Float(1)),sympy.Float(2)))
(a + 1.0)**2.0
>>> sympy.expand(sympy.Pow(sympy.Add(_HI,sympy.Float(1)),sympy.Integer(2)))
a**2 + 2.0*a + 1.0
>>>
phcreery commented

Here is a little fix I came up with. Line 133 of phcreery@0984fe9 I don't see this hurting anything. Let me know what you think.

stefnotch commented

Sorry for the late response. I took a look at this and yes, it does seem like the current default behavior is not ideal.
https://docs.sympy.org/latest/gotchas.html#evaluating-expressions-with-floats-and-rationals

Instead, we should almost always use the Integer and Rational data types. I think the conversions in Sympy should always work out the right way.

One minor gotcha of that approach is that the Integer and Rational data types can become arbitrarily large. That means if someone types 99999999**9999999, Sympy will painstakingly try to compute the entire result, regardless of how long it takes. To "fix" that, we have to interrupt the execution after a few seconds.